ssh-keygen -f

ssh-keygen -f ~/.ssh/id_rsa -p
https://wiki.archlinux.org/title/SSH_keys#Changing_the_private_key's_passphrase_without_changing_the_key

See also

• ssh-keygen [ -R, -t | -p | -i | -y | -f | ~/.ssh/id_rsa | --help ] ~/.ssh/known_hosts}